The leading Republican candidate in the U.S. Senate race, Mack earned national media exposure stumping across the state for Mitt Romney. The former Massachusetts governor went so far as to anoint the 44-year-old Mack in campaign stops as "the next senator from Florida."

That endorsement helped drive Mack's opponent, Adam Hasner, out of the race this week and into a congressional race in South Florida. Another GOP challenger, Craig Miller, exited to run for a congressional seat, too, leaving only former Sen. George LeMieux as a serious challenger.

Other Republican candidates may remain in the race, but Mack is acting the part of frontrunner, and is backed up by polls. Among likely Republican voters, Mack leads LeMieux 38 percent to 12 percent, according to a Tampa Bay Times/Miami Herald/Bay News 9 poll last week. Mike McCalister registered 7 percent in the poll.

Mack has aimed his campaign rhetoric squarely at the incumbent Democrat, Sen. Bill Nelson, 69, whose last election was his 2006 trouncing of then-U.S. Rep. Katherine Harris, the state's former Secretary of State.

Mack supported Romney in 2008, too. But he called the week he spent on the campaign trail with Romney "a huge benefit" in developing a relationship with a presidential campaign that will also be running hard in Florida.

"I had the opportunity to be with the guy who won the primary, and to work with him and on his behalf," he said.

It certainly got him attention in a big state with multiple media markets, where campaigns are won and lost on television, and require healthy fundraising to pay for it all.

As a Romney surrogate, Mack did two local television appearances from Fort Myers on the day of the primary. He did eight additional regional or local television appearances, and then appeared on FOX News in the evening. Along with his wife, Republican Rep. Mary Bono Mack of California, Mack appeared on CNN's Piers Morgan show at midnight. And on Wednesday morning, he was on CNN, CNBC and MSNBC.

It's in marked contrast to Nelson, who was absent when President Barack Obama traveled to Orlando last month to announce a tourism jobs initiative at Disney World.

Nelson's campaign had no comment Tuesday on the reshuffled GOP Senate field. The poll shows Nelson with a three-point lead over Rep. Connie Mack, R-Fort Myers, 45 percent to 42 percent. Other polls have similar findings. A Jan. 11 Quinnipiac University poll had Nelson up 41 percent to Mack's 40.

"The election's still 10 months away and Bill's just focused on doing his job," said Nelson's campaign spokesman, Christian Robinson. "The politics will take care of itself."

The Republican race has clearly solidified as a two-person race between Mack and LeMieux, said pollster Brad Coker of Mason-Dixon Polling & Research, the nonpartisan, Jacksonville-based company that conducted the Times/Herald/Bay News 9 poll.

"Long term, I think it makes Mack even stronger — particularly in light of Romney's strong showing," Coker said. "It doesn't look like Florida Republicans are looking for an 'outsider, insurgent' conservative, but rather the most electable candidate with basic conservative credentials."

Coker said it would be difficult for LeMieux to paint himself as a more conservative alternative to Mack, given his ties to former Gov. Charlie Crist.

"He's basically viewed as the guy who was willing to go to D.C. on a short term basis to keep the Senate seat warm for Charlie Crist," Coker said. "Given Crist's demise within the Republican Party, being the former governor's lap dog doesn't give LeMieux much street credibility to make the conservative outsider case."

For all of the candidates, the next challenge is to raise money. Mack, who raised $758,394 since getting in the race and has $917,925 on hand, will be focused catching up with Nelson. The Democratic senator has banked $8.5 million for his re-election bid — reportedly more than any other senator of his party running this year. Nelson raised $1.4 million during the final three months of 2011, the campaign said last month.

Mack says he's confident he can catch up.

"We've got a lot of work to do, but we're working every day," he said. "And I'm confident that by the time we get to that window where you start to spend a lot more of that money that you've raised, that we will be in a position and have the resources to be competitive. And hopefully to win."